With the progression of various genome projects, sequences of the entire genomes of organisms have become available. The flood of data has raised the interests of many investigators. One of the more noticeable discoveries was the observation that the human genome does not code for significantly more genes than the genome of simple organisms such as the fruit fly.
The focus of many investigators is now shifting from the identification of genes to the determination of gene expression and gene function. Examples of such technologies are DNA microarrays, functional genomics applications, and proteomics. One thing these technologies have in common is that they center around the function and expression of coding sequences.
However, while our knowledge of genes is increasing dramatically, the understanding of how the expression of the genes is regulated is limiting the ability to apply this rapidly increasing knowledge. This is, for instance, the case in the generation of transgenic plants and animals and in human gene therapy. In these applications, foreign nucleic acid is typically introduced into cells to obtain expression of coding sequences. Often, integration of the foreign nucleic acid into the cell's genome is required for prolonged function of the introduced sequences. However, integration of sequences into the genome leads to unpredictability of expression because the surrounding DNA influences the transcription of the integrated sequences. This unpredictability is due, in part, to the fact that introduced sequences cannot yet be provided with sufficient genetic information to functionally isolate the integrated sequences from the transcription influencing effects of the surrounding DNA. Also, this is due to the fact that not enough is known about the transcription influencing effects of surrounding DNA.